Squid 3.1.1 release notes

Squid Developers

This document contains the release notes for version 3.1 of Squid.
Squid is a WWW Cache application developed by the National Laboratory
for Applied Network Research and members of the Web Caching community.

A large number of the show-stopper bugs have been fixed along with general improvements to the ICAP support.
While this release is not fully bug-free we believe it is ready for use in production on many systems.

We welcome feedback and bug reports. If you find a new bug, please see
http://wiki.squid-cache.org/SquidFaq/BugReporting for how to submit a report with a stack trace and other required details. Additional information is also very welcome on other open bugs.

Begining with 3.1 the Squid Developers are using a new release numbering system.

We have decided, based on input from interested users to drop the Squid-2 terminology of
(DEVEL, PRE, RC, and STABLE) from the release package names.
These are replaced with a simpler 3-tier system based around the natural code development cycle.

Daily generated snapshots of all current versions are provided as testing (old DEVEL) and bug-fix releases.
These are numbered from their last release with a date appended.
Snapshots generated from 3.HEAD continue to be highly volatile.

Regular feature releases from Squid-3 will be branched out as sub-versions. Such as this Squid-3.1.

All this is previous policy you should be accustomed to. Now we get to the new numbering change.

Initial branch packages will be generated with a 3.X.0.Z version as testing packages.
Packages and Snapshots generated with these 3-dot numbers are expected to be relatively stable regarding feature behaviors.
Suitable for testing, but without any guarantees under production loads. This replaces both the old PRE and RC packages.

If a large number of bugs are found several *.0.Z packages may be attempted before any is considered production-ready.

When one of these Squid-3.X.0.Z packages passes our bug-free standards a 3.X.Y numbered release will be made.

We can only hope enough testing has been done to consider these ready for production use.
As always we are fully dependent on people testing the previous packages and reporting all bugs.

In support of all this are several squid-dev process changes which have been worked out over the last year.

We no longer accept new features into branches.
Those are reserved for the next feature release.
The cycle for major releases is hoped to be fast enough to suit some peoples needs for new features
and others need for stability in the branched releases.

We now audit and vote on all feature and major code additions.
Requiring at least two sets of developer eyes on any new features before they are committed to 3.HEAD.
Vastly reducing the number of bugs in all code.

Don't worry, few operational changes have been made.
Older configs from Squdi 2.x and 3.0 are still expected to run in 3.1 with only the usual minor
changes seen between major release. Details on those are listed below.

New users will be relieved to see a very short squid.conf on clean installs.
Many of the options have reasonable defaults but had previously needed them explicitly configured!
These are now proper built-in defaults and no longer need to be in squid.conf unless changed.

All of the option documentation has been offloaded to another file squid.conf.documented which
contains a fully documented set of available options previously cluttering up squid.conf itself.

Package maintainers are provided with a second file squid.conf.default which as always contains the default
config options provided on a clean install.

We are also providing online copies of configuration documentation.
Updated live to match the latest release of each Squid series, and a combined global version.
This is available on
the Squid website

New Features for IPv6

Squid handles localhost values seperately. For the purpose of ACLs and also external
connections ::1 is considered a seperate IP from 127.0.0.1. This means all ACL which
define behaviour for localhost may need ::1/128 included.

Pinger has been upgraded to perform both ICMP and ICMPv6 as required.
As a result of this and due to a change in the binary protocol format between them,
new builds of Squid are no longer backwards-compatible with old pinger binaries.
You will need to perform "make install-pinger" again after installing Squid.

Peer and Client SNMP tables have been altered to handle IPv6 addresses.
As a side effect of this the long-missing fix to show seperate named peers on one IP
has been integrated. Making the SNMP peer table now produce correct output.
The table structure change is identical for both IPv4-only and Dual modes but with
IPv4-only simply not including any IPv6 entries. This means any third-party SNMP
software which hard coded the MIB paths needs to be upgraded for this Squid release.
Details can be found in the wiki
SNMP feature page.

Limitations of IPv6 Support

In this release there is no split-stack support. This means that OS which do not provide
IP stacks based on the KAME stack with Hybrid extensions to do IPv4-mapping cannot use IPv6
with Squid.

Specify a specific tcp_outgoing_address and the clients who match its ACL are limited
to the IPv4 or IPv6 network that address belongs to. They are not permitted over the
IPv4-IPv6 boundary. Some ACL voodoo can however be applied to explicitly route the
IPv6/IPv4 bound traffic (DIRECT access) out an appropriate interface.
See the squid.conf documentation for further details.

WCCP is not available (neither version 1 or 2).
It remains built into squid for use with IPv4 traffic but IPv6 cannot use it.

Pseudo-Transparent Interception is done via NAT at the OS level and is not available in IPv6.
Squid will ensure that any port set with transparent or intercept options be an IPv4-only
listening address. Wildcard can still be used but will not open as an IPv6.
To ensure that squid can accept IPv6 traffic on its default port, an alternative should
be chosen to handle transparently intercepted traffic.

http_port 3128
http_port 8080 intercept

Real transparent Interception (TPROXY) may be able to perform IPv6 interception.
However this currently still needs kernel patching with experimental patches to enable IPv6.
Squid will attempt to discover support on startup and may permit or deny IPv6 wildcard for
tproxy flagged ports depending on your system.

The bundled NTLM Auth helper is IPv4-native between itself and the NTLM server.
A new one will be needed for IPv6 traffic between the helper and server.

The bundled RADIUS Auth helper is IPv4-native, both in traffic between and data storage
with the RADIUS server. A new helper will be needed for IPv6 RADIUS protocol.

Zero Penalty Hit created a patch to set QoS markers on outgoing traffic.

Allows you to select a TOS/Diffserv value to mark local hits.

Allows you to select a TOS/Diffserv value to mark peer hits.

Allows you to selectively mark only sibling or parent requests

Allows any HTTP response towards clients to have the TOS value of the response coming from
the remote server preserved.
For this to work correctly, you will need to patch your linux kernel with the TOS preserving ZPH patch.
The kernel patch can be downloaded from
http://zph.bratcheda.org

Allows you to mask certain bits in the TOS received from the remote server,
before copying the value to the TOS send towards clients.

Squid Configuration

Squid 3.1 needs to be configured with --enable-zph-qos for the ZPH QoS controls to be available.

The configuration options for Squid 2.7 and 3.1 are based on different ZPH patches.
The two releases configuration differs and only the TOS mode settings are directly translatable.

qos_flows local-hit=0xff Responses found as a HIT in the local cache

qos_flows sibling-hit=0xff Responses found as a HIT in a sibling peer

qos_flows parent-hit=0xff Responses found as a HIT in a parent peer

The lines above are separated for documentation. qos_flows may be configured with all options on one line, or separated as shown.
Also options may be repeated as many times as desired. Only the final configured value for any option will be used.

The legacy Option and Priority modes available in Squid-2.7 are no longer supported.

Squid-in-the-middle decryption and encryption of CONNECT tunneled SSL traffic,
using configurable client- and server-side certificates.
While decrypted, the traffic can be inspected using ICAP.

Squid 3.1 releases limit SSL Bump to CONNECT requests and requires that clients are
configured to explicitly use the proxy in their browser settings or via WPAD/PAC
configuration. Use of interception for port 443 is not officially supported, despite
being known to work under certain limited networking circumstances.

ICAP is now extended with full bypass and dynamic chain routing to handle multiple
adaptation services.

ICAP Adaptation Service Sets and Chains

An adaptation service set contains similar, interchangeable services. No more
than one service is successfully applied. If one service is down or fails,
Squid can use another service. Think "hot standby" or "spare" ICAP servers.

Sets may seem similar to the existing "service bypass" feature, but they allow
the failed adaptation to be retried and succeed if a replacement service is
available. The services in a set may be all optional or all essential,
depending on whether ignoring the entire set is acceptable. The mixture of
optional and essential services in a set is supported, but yields results that
may be difficult for a human to anticipate or interpret. Squid warns when it
detects such a mixture.

When performing adaptations with a set, failures at a service (optional or
essential, does not matter) are retried with a different service if possible.
If there are no more replacement services left to try, the failure is treated
depending on whether the last service tried was optional or essential: Squid
either tries to ignore the failure and proceed or terminates the master
transaction.

An adaptation chain is a list of different services applied one after another,
forming an adaptation pipeline. Services in a chain may be optional or
essential. When performing adaptations, failures at an optional service are
ignored as if the service did not exist in the chain.

Request satisfaction terminates the adaptation chain.

When forming a set or chain for a given transaction, optional down services are ignored as if they did not exist.

ICAP and eCAP services can be mixed and matched in an adaptation set or chain.

Dynamically form adaptation chains based on the ICAP X-Next-Services header.

If an ICAP service with the routing=1 option in squid.conf returns an ICAP
X-Next-Services response header during a successful REQMOD or RESPMOD
transaction, Squid abandons the original adaptation plan and forms a new
adaptation chain consisting of services identified in the X-Next-Services
header value (using a comma-separated list of adaptation service names from
squid.conf). The dynamically created chain is destroyed once the new plan is
completed or replaced.

This feature is useful when a custom adaptation service knows which other
services are applicable to the message being adapted.

Limit adaptation iterations to adaptation_service_iteration_limit to protect
Squid from infinite adaptation loops caused by ICAP services constantly
including themselves in the dynamic adaptation chain they request. When the
limit is exceeded, the master transaction fails. The default limit of 16
should be large enough to not require an explicit configuration in most
environments yet may be small enough to limit side-effects of loops.

Squid-3.1 adds native support for streaming protocol ICY.
Also commonly known as SHOUTcast multimedia streams.

This protocol uses port 80 and violates RFC 2616 by using an HTTP/1.1 compliant request and non-HTTP reply
to start the stream transaction. If the reply is handled according to HTTP/1.1 RFC-compliance requirements
the audio stream becomes jerky and contains regular 'popping' sounds.

Squid now processes the ICY replies natively according to the ICY requirements, not HTTP/1.1 requirements.
The streamed data is not cacheable. All processing and access controls may be applied the same as for HTTP.

squid.conf change

Squid-2 contained a hack using the update_http0.9 squid.conf option to work around the
unusual replies. This option is now obsolete.

The proto ACL type matches ICY once the reply has been received, before that the processing
is only aware on an HTTP request. So the ACL will match HTTP.

Whether to use any result found by follow_x_forwarded_for in further ACL processing.
Default: ON

Controls whether the indirect client address
(see follow_x_forwarded_for) is used instead of the
direct client address in acl matching.

adaptation_access

Sends an HTTP transaction to an ICAP or eCAP adaptation service.

adaptation_access service_name allow|deny [!]aclname...
adaptation_access set_name allow|deny [!]aclname...
At each supported vectoring point, the adaptation_access
statements are processed in the order they appear in this
configuration file. Statements pointing to the following services
are ignored (i.e., skipped without checking their ACL):
- services serving different vectoring points
- "broken-but-bypassable" services
- "up" services configured to ignore such transactions
(e.g., based on the ICAP Transfer-Ignore header).
When a set_name is used, all services in the set are checked
using the same rules, to find the first applicable one. See
adaptation_service_set for details.
If an access list is checked and there is a match, the
processing stops: For an "allow" rule, the corresponding
adaptation service is used for the transaction. For a "deny"
rule, no adaptation service is activated.
It is currently not possible to apply more than one adaptation
service at the same vectoring point to the same HTTP transaction.

adaptation_masterx_shared_names

For each master transaction (i.e., the HTTP request and response
sequence, including all related ICAP and eCAP exchanges), Squid
maintains a table of metadata. The table entries are (name, value)
pairs shared among eCAP and ICAP exchanges. The table is destroyed
with the master transaction.
This option specifies the table entry names that Squid must accept
from and forward to the adaptation transactions.
An ICAP REQMOD or RESPMOD transaction may set an entry in the
shared table by returning an ICAP header field with a name
specified in adaptation_masterx_shared_names. Squid will store
and forward that ICAP header field to subsequent ICAP
transactions within the same master transaction scope.
Only one shared entry name is supported at this time.

adaptation_service_chain

Configures a list of complementary services that will be applied
one-by-one, forming an adaptation chain or pipeline. This is useful
when Squid must perform different adaptations on the same message.
adaptation_service_chain chain_name service_name1 svc_name2 ...
The named services are used in the chain declaration order. The first
applicable adaptation service from the chain is used first. The next
applicable service is applied to the successful adaptation results of
the previous service in the chain.
When adaptation starts, broken services are ignored as if they were
not a part of the chain. A broken service is a down optional service.
Request satisfaction terminates the adaptation chain because Squid
does not currently allow declaration of RESPMOD services at the
"reqmod_precache" vectoring point (see icap_service or ecap_service).
The services in a chain must be attached to the same vectoring point
(e.g., pre-cache) and use the same adaptation method (e.g., REQMOD).
A chain may contain a mix of optional and essential services. If an
essential adaptation fails (or the failure cannot be bypassed for
other reasons), the master transaction fails. Otherwise, the failure
is bypassed as if the failed adaptation service was not in the chain.

adaptation_service_iteration_limit

Limits the number of iterations allowed when applying adaptation
services to a message. If your longest adaptation set or chain
may have more than 16 services, increase the limit beyond its
default value of 16. If detecting infinite iteration loops sooner
is critical, make the iteration limit match the actual number
of services in your longest adaptation set or chain.
Infinite adaptation loops are most likely with routing services.

adaptation_service_set

Configures an ordered set of similar, redundant services. This is
useful when hot standby or backup adaptation servers are available.
adaptation_service_set set_name service_name1 service_name2 ...
The named services are used in the set declaration order. The first
applicable adaptation service from the set is used first. The next
applicable service is tried if and only if the transaction with the
previous service fails and the message waiting to be adapted is still
intact.
When adaptation starts, broken services are ignored as if they were
not a part of the set. A broken service is a down optional service.
The services in a set must be attached to the same vectoring point
(e.g., pre-cache) and use the same adaptation method (e.g., REQMOD).
If all services in a set are optional then adaptation failures are
bypassable. If all services in the set are essential, then a
transaction failure with one service may still be retried using
another service from the set, but when all services fail, the master
transaction fails as well.
A set may contain a mix of optional and essential services, but that
is likely to lead to surprising results because broken services become
ignored (see above), making previously bypassable failures fatal.
Technically, it is the bypassability of the last failed service that
matters.

adapted_http_access

New name for http_access2. This form includes access control
of ICAP and eCAP adaptations as well as the URL-rewriter alterations.

A broken or confused HTTP/1.1 client may send a chunked HTTP
request to Squid. Squid does not have full support for that
feature yet. To cope with such requests, Squid buffers the
entire request and then dechunks request body to create a
plain HTTP/1.0 request with a known content length. The plain
request is then used by the rest of Squid code as usual.
The option value specifies the maximum size of the buffer used
to hold the request before the conversion. If the chunked
request size exceeds the specified limit, the conversion
fails, and the client receives an "unsupported request" error,
as if dechunking was disabled.
Dechunking is enabled by default. To disable conversion of
chunked requests, set the maximum to zero.
Request dechunking feature and this option in particular are a
temporary hack. When chunking requests and responses are fully
supported, there will be no need to buffer a chunked request.

delay_pool_uses_indirect_client

Whether to use any result found by follow_x_forwarded_for in delay_pool assignment.
Default: ON

Controls whether the indirect client address
(see follow_x_forwarded_for) is used instead of the
direct client address in delay pools.

dns_v4_fallback

New option to prevent squid from always looking up IPv4 regardless of whether IPv6 addresses are found.
Squid will follow a policy of prefering IPv6 links, keeping the IPv4 only as a safety net behind IPv6.

Standard practice with DNS is to lookup either A or AAAA records
and use the results if it succeeds. Only looking up the other if
the first attempt fails or otherwise produces no results.
That policy however will cause squid to produce error pages for some
servers that advertise AAAA but are unreachable over IPv6.
If this is ON squid will always lookup both AAAA and A, using both.
If this is OFF squid will lookup AAAA and only try A if none found.
WARNING: There are some possibly unwanted side-effects with this on:
*) Doubles the load placed by squid on the DNS network.
*) May negatively impact connection delay times.

ecap_enable

Controls whether eCAP support is enabled. Default: OFF

ecap_service

Defines a single eCAP service

ecap_service servicename vectoring_point bypass service_url
vectoring_point = reqmod_precache|reqmod_postcache|respmod_precache|respmod_postcache
This specifies at which point of transaction processing the
eCAP service should be activated. *_postcache vectoring points
are not yet supported.
bypass = 1|0
If set to 1, the eCAP service is treated as optional. If the
service cannot be reached or malfunctions, Squid will try to
ignore any errors and process the message as if the service
was not enabled. No all eCAP errors can be bypassed.
If set to 0, the eCAP service is treated as essential and all
eCAP errors will result in an error page returned to the
HTTP client.
service_url = ecap://vendor/service_name?custom&cgi=style&parameters=optional
Example:
ecap_service service_1 reqmod_precache 0 ecap://filters-R-us/leakDetector?on_error=block
ecap_service service_2 respmod_precache 1 icap://filters-R-us/virusFilter?config=/etc/vf.cfg

New option to replace the old configure option --enable-default-err-language
New translations can be downloaded from http://www.squid-cache.org/Versions/langpack/

Set the default language which squid will send error pages in
if no existing translation matches the clients language
preferences.
If unset (default) generic English will be used.

error_log_languages

Log to cache.log what languages users are attempting to
auto-negotiate for translations.
Successful negotiations are not logged. Only failures
have meaning to indicate that Squid may need an upgrade
of its error page translations.

follow_x_forwarded_for

Enable processing of the X-Forwarded-for header for various administration tasks.

Allowing or Denying the X-Forwarded-For header to be followed to
find the original source of a request.
Requests may pass through a chain of several other proxies
before reaching us. The X-Forwarded-For header will contain a
comma-separated list of the IP addresses in the chain, with the
rightmost address being the most recent.
If a request reaches us from a source that is allowed by this
configuration item, then we consult the X-Forwarded-For header
to see where that host received the request from. If the
X-Forwarded-For header contains multiple addresses, and if
acl_uses_indirect_client is on, then we continue backtracking
until we reach an address for which we are not allowed to
follow the X-Forwarded-For header, or until we reach the first
address in the list. (If acl_uses_indirect_client is off, then
it's impossible to backtrack through more than one level of
X-Forwarded-For addresses.)
The end result of this process is an IP address that we will
refer to as the indirect client address. This address may
be treated as the client address for access control, delay
pools and logging, depending on the acl_uses_indirect_client,
delay_pool_uses_indirect_client and log_uses_indirect_client
options.
SECURITY CONSIDERATIONS:
Any host for which we follow the X-Forwarded-For header
can place incorrect information in the header, and Squid
will use the incorrect information as if it were the
source address of the request. This may enable remote
hosts to bypass any access control restrictions that are
based on the client's source addresses.
For example:
acl localhost src 127.0.0.1
acl my_other_proxy srcdomain .proxy.example.com
follow_x_forwarded_for allow localhost
follow_x_forwarded_for allow my_other_proxy

ftp_epsv

FTP Protocol extensions permit the use of a special "EPSV" command.
NATs may be able to put the connection on a "fast path" through the
translator using EPSV, as the EPRT command will never be used and therefore,
translation of the data portion of the segments will never be needed.
Turning this OFF will prevent EPSV being attempted.
WARNING: Doing so will convert Squid back to the old behavior with all
the related problems with external NAT devices/layers.
Requires ftp_passive to be ON (default) for any effect.

ftp_epsv_all

FTP Protocol extensions permit the use of a special "EPSV ALL" command.
NATs may be able to put the connection on a "fast path" through the
translator, as the EPRT command will never be used and therefore,
translation of the data portion of the segments will never be needed.
When a client only expects to do two-way FTP transfers this may be useful.
If squid finds that it must do a three-way FTP transfer after issuing
an EPSV ALL command, the FTP session will fail.
If you have any doubts about this option do not use it.
Squid will nicely attempt all other connection methods.
Requires ftp_passive to be ON (default)

forward_max_tries

Controls how many different forward paths Squid will try
before giving up. Default: 10

icap_log

New option to write ICAP log files record ICAP transaction summaries, one line per
transaction. Similar to access.log.

The icap_log option format is:
icap_log <filepath> [<logformat name> [acl acl ...]]
icap_log none [acl acl ...]]
Please see access_log option documentation for details. The two
kinds of logs share the overall configuration approach and many
features.
ICAP processing of a single HTTP message or transaction may
require multiple ICAP transactions. In such cases, multiple
ICAP transaction log lines will correspond to a single access
log line.
ICAP log uses logformat codes that make sense for an ICAP
transaction. Header-related codes are applied to the HTTP header
embedded in an ICAP server response, with the following caveats:
For REQMOD, there is no HTTP response header unless the ICAP
server performed request satisfaction. For RESPMOD, the HTTP
request header is the header sent to the ICAP server. For
OPTIONS, there are no HTTP headers.
The following format codes are also available for ICAP logs:
icap::<A ICAP server IP address. Similar to <A.
icap::<service_name ICAP service name from the icap_service
option in Squid configuration file.
icap::ru ICAP Request-URI. Similar to ru.
icap::rm ICAP request method (REQMOD, RESPMOD, or
OPTIONS). Similar to existing rm.
icap::>st Bytes sent to the ICAP server (TCP payload
only; i.e., what Squid writes to the socket).
icap::<st Bytes received from the ICAP server (TCP
payload only; i.e., what Squid reads from
the socket).
icap::tr Transaction response time (in
milliseconds). The timer starts when
the ICAP transaction is created and
stops when the transaction is completed.
Similar to tr.
icap::tio Transaction I/O time (in milliseconds). The
timer starts when the first ICAP request
byte is scheduled for sending. The timers
stops when the last byte of the ICAP response
is received.
icap::to Transaction outcome: ICAP_ERR* for all
transaction errors, ICAP_OPT for OPTION
transactions, ICAP_ECHO for 204
responses, ICAP_MOD for message
modification, and ICAP_SAT for request
satisfaction. Similar to Ss.
icap::Hs ICAP response status code. Similar to Hs.
icap::>h ICAP request header(s). Similar to >h.
icap::<h ICAP response header(s). Similar to <h.
The default ICAP log format, which can be used without an explicit
definition, is called icap_squid:
logformat icap_squid %ts.%03tu %6icap::tr %>a %icap::to/%03icap::Hs %icap::<size %icap::rm %icap::ru% %un -/%icap::<A -

icap_retry

New option to determine which retriable ICAP transactions are
retried.

Transactions that received a complete ICAP response
and did not have to consume or produce HTTP bodies to receive
that response are usually retriable.
icap_retry allow|deny [!]aclname ...
Squid automatically retries some ICAP I/O timeouts and errors
due to persistent connection race conditions.

icap_retry_limit

Limits the number of retries allowed. When set to zero (default),
no retries are allowed.
Communication errors due to persistent connection race
conditions are unavoidable, automatically retried, and do not
count against this limit.

New option to import entire secondary configuration files into squid.conf.

Squid will follow the files immediately and insert all their content
as if it was at that position in squid.conf. As per squid.conf some
options are order-specific within the config as a whole.
A few layers of include are allowed, but too many are confusing and
squid will enforce an include depth of 16 files.
Syntax:
include /path/to/file1 /path/to/file2

This options allows you to control which requests get logged
to icap.log. See the icap_log directive for ICAP log details.

log_uses_indirect_client

Whether to use any result found by follow_x_forwarded_for in access.log.
Default: ON

Controls whether the indirect client address
(see follow_x_forwarded_for) is used instead of the
direct client address in the access log.

netdb_filename

A filename where Squid stores it's netdb state between restarts.
To disable, enter "none".

pinger_enable

New option to enable/disable the ICMP pinger helper with a reconfigure instead of a full rebuild.

Control whether the pinger is active at run-time.
Enables turning ICMP pinger on and off with a simple squid -k reconfigure.
default is off when --enable-icmp is compiled in.

ssl_bump

New Access control for which CONNECT requests to an http_port
marked with an sslBump flag are actually "bumped". Please
see the sslBump flag of an http_port option for more details
about decoding proxied SSL connections.
DEFAULT: No requests are bumped.

For example, the following lines will bypass all validation errors
when talking to servers located at 172.16.0.0/16. All other
validation errors will result in ERR_SECURE_CONNECT_FAIL error.
acl BrokenServersAtTrustedIP dst 172.16.0.0/16
sslproxy_cert_error allow BrokenServersAtTrustedIP
sslproxy_cert_error deny all
This option must use fast ACL expressions only. Expressions that use
external lookups or communication result in unpredictable behavior or
crashes.
Without this option, all server certificate validation errors
terminate the transaction. Bypassing validation errors is dangerous
because an error usually implies that the server cannot be trusted and
the connection may be insecure.

qos_flows local-hit= sibling-hit= parent-hit=

Allows you to select a TOS/DSCP value to mark outgoing
connections with, based on where the reply was sourced.
TOS values really only have local significance - so you should
know what you're specifying. For more information, see RFC2474,
RFC2475, and RFC3260.
The TOS/DSCP byte must be exactly that - octet value 0x00-0xFF.
Note that in practice often only values up to 0x3F are usable
as the two highest bits have been redefined for use by ECN
(RFC3168).
This setting is configured by setting the source TOS values:
local-hit=0xFF Value to mark local cache hits.
sibling-hit=0xFF Value to mark hits from sibling peers.
parent-hit=0xFF Value to mark hits from parent peers.
NOTE: 'miss' preserve feature is only possible on Linux at this time.
For the following to work correctly, you will need to patch your
linux kernel with the TOS preserving ZPH patch.
The kernel patch can be downloaded from http://zph.bratcheda.org
disable-preserve-miss
If set, any HTTP response towards clients will
have the TOS value of the response comming from the
remote server masked with the value of miss-mask.
miss-mask=0xFF
Allows you to mask certain bits in the TOS received from the
remote server, before copying the value to the TOS sent
towards clients.
Default: 0xFF (TOS from server is not changed).

NTLM: The helper binary bundled with Squid under the name ntlm_auth has been renamed to accurately reflect
its real behavior and to prevent confusion with the more useful Samba helper using the same name.

Despite being used for NTLM, the helper does not in fact provide true NTLM function. What it does provide is
SMB LanManager authentication through the NTLM interface without the need for a domain controller. Thus the
new name is ntlm_smb_lm_auth.

WARNING: due to the name clash with Samba helper, admin should be careful to only update their squid.conf if the
squid bundled binary is used and needed. If the Samba helper is in use, the squid.conf should not be altered.

balance_on_multiple_ip

The previous default behavour (rotate per-request) of this setting causes failover clashes with IPv6 built-in mechanisms.
It has thus been turned off by default. Making the 'best choice' IP continue in use for any hostname until it encounters a connection failure and failover drops to the next known IP.

Modern IP resolvers in squid sort lookup results by preferred access.
By default squid will use these IP in order and only rotates to
the next listed when the most preffered fails.
Some load balancing servers based on round robin DNS have been
found not to preserve user session state across requests
to different IP addresses.
Enabling this directive Squid rotates IP's per request.

use 'htcp-no-clr' to send HTCP to the neighbor but without
sending any CLR requests. This cannot be used with
htcp-only-clr.
use 'htcp-no-purge-clr' to send HTCP to the neighbor
including CLRs but only when they do not result from
PURGE requests.
use 'htcp-only-clr' to send HTCP to the neighbor but ONLY
CLR requests. This cannot be used with htcp-no-clr.
use 'htcp-forward-clr' to forward any HTCP CLR requests
this proxy receives to the peer.
use 'connection-auth=off' to tell Squid that this peer does
not support Microsoft connection oriented authentication,
and any such challenges received from there should be
ignored. Default is 'auto' to automatically determine the
status of the peer.
use 'connect-fail-limit=nn' to specify how many times
connecting to a peer must fail before it is marked as
down. Default is 10.
use 'no-tproxy' to specify that requests passed to this peer
are not to have the client IP spoofed. For use to prevent
packet routing issues with a cluster of peers behind WCCPv2.
multicast-siblings ported from 2.7

Now an optional entry in squid.conf. If present it will force all visitors to receive the error pages
contained in the directory it points at. If absent, error page localization will be given a chance.

If you wish to create your own versions of the default
error files to customize them to suit your company COPY
the error/template files to another directory and point
this tag at them.
WARNING: This option will disable multi-language support
on error pages if used.

debug_options rotate=

New parameter rotate=N to control number of cache.log rotations independent of other logs.

external_acl_type

New options 'ipv4' and 'ipv6' are added to set the IPv4/v6 protocol between squid and its helpers.
Please be aware of some limits to these options. These options only affet the transport protocol used
to send data to and from the helpers. Squid in IPv6-mode may still send %SRC addresses in IPv4 or IPv6
format, so all helpers will need to be checked and converted to cope with such information cleanly.

ipv4 / ipv6 IP-mode used to communicate to this helper.
For compatability with older configurations and helpers
the default is 'ipv4'.

New header input format specifiers. To seperate Request and Reply headers when both passed back.

If set to "transparent", Squid will not alter the
X-Forwarded-For header in any way.
If set to "delete", Squid will delete the entire
X-Forwarded-For header.
If set to "truncate", Squid will remove all existing
X-Forwarded-For entries, and place itself as the sole entry.

Option 'transparent' is being deprecated in favour of 'intercept' which more clearly identifies what the option does.
For now option 'tproxy' remains with old behaviour meaning fully-invisible proxy using TPROXY support.

New port options

intercept Rename of old 'transparent' option to indicate proper functionality.
allow-direct Allow direct forwarding in accelerator mode. Normally
accelerated requests are denied direct forwarding as if
never_direct was used.
connection-auth[=on|off]
use connection-auth=off to tell Squid to prevent
forwarding Microsoft connection oriented authentication
(NTLM, Negotiate and Kerberos)
keepalive[=idle,interval,timeout]
Enable TCP keepalive probes of idle connections
idle is the initial time before TCP starts probing
the connection, interval how often to probe, and
timeout the time before giving up.
ignore-cc Ignore request Cache-Control headers.
Warning: This option violates HTTP specifications if
used in non-accelerator setups.
sslBump Intercept each CONNECT request matching ssl_bump ACL,
establish secure connection with the client and with
the server, decrypt HTTP messages as they pass through
Squid, and treat them as unencrypted HTTP messages,
becoming the man-in-the-middle.
When this option is enabled, additional options become
available to specify SSL-related properties of the
client-side connection: cert, key, version, cipher,
options, clientca, cafile, capath, crlfile, dhparams,
sslflags, and sslcontext. See the https_port directive
for more information on these options.
The ssl_bump option is required to fully enable
the SslBump feature.

https_port intercept sslbump connection-auth[=on|off]

New port options. see http_port.

icap_service bypass=on|off|1|0 routing=on|off|1|0

New options 'bypass=' and 'routing='.

bypass=on|off|1|0
If set to 'on' or '1', the ICAP service is treated as
optional. If the service cannot be reached or malfunctions,
Squid will try to ignore any errors and process the message as
if the service was not enabled. No all ICAP errors can be
bypassed. If set to 0, the ICAP service is treated as
essential and all ICAP errors will result in an error page
returned to the HTTP client.
Bypass is off by default: services are treated as essential.
routing=on|off|1|0
If set to 'on' or '1', the ICAP service is allowed to
dynamically change the current message adaptation plan by
returning a chain of services to be used next. The services
are specified using the X-Next-Services ICAP response header
value, formatted as a comma-separated list of service names.
Each named service should be configured in squid.conf and
should have the same method and vectoring point as the current
ICAP transaction. Services violating these rules are ignored.
An empty X-Next-Services value results in an empty plan which
ends the current adaptation.
Routing is not allowed by default: the ICAP X-Next-Services
response header is ignored.

New log format tag sets %icap::* %adapt::* for adaptation information.
%Hs tag deprecated and replaced by request/reply specific >Hs and <Hs
new %>ha option to log HTTP request headers after adaptation and redirection.
HTTP request/reply format tags may now be optionally prefixed with http::.
Old forms will be deprecated in some as yet undecided future release.

dt Total time spent making DNS lookups (milliseconds)
[http::]>ha The HTTP request headers after adaptation and redirection.
[http::]>Hs HTTP status code sent to the client
[http::]<Hs HTTP status code received from the next hop
[http::]>sh Received HTTP request headers size
[http::]<sh Sent HTTP reply headers size
[http::]<pt Peer response time in milliseconds. The timer starts
when the last request byte is sent to the next hop
and stops when the last response byte is received.
[http::]<tt Total server-side time in milliseconds. The timer
starts with the first connect request (or write I/O)
sent to the first selected peer. The timer stops
with the last I/O with the last peer.
If ICAP is enabled, the following two codes become available (as
well as ICAP log codes documented with the icap_log option):
icap::tt Total ICAP processing time for the HTTP
transaction. The timer ticks when ICAP
ACLs are checked and when ICAP
transaction is in progress.
icap::<last_h The header of the last ICAP response
related to the HTTP transaction. Like
<h, accepts an optional header name
argument. Will not change semantics
when multiple ICAP transactions per HTTP
transaction are supported.
If adaptation is enabled the following two codes become available:
adapt::sum_trs Summed adaptation transaction response
times recorded as a comma-separated list in
the order of transaction start time. Each time
value is recorded as an integer number,
representing response time of one or more
adaptation (ICAP or eCAP) transaction in
milliseconds. When a failed transaction is
being retried or repeated, its time is not
logged individually but added to the
replacement (next) transaction.
adapt::all_trs All adaptation transaction response times.
Same as adaptation_strs but response times of
individual transactions are never added
together. Instead, all transaction response
times are recorded individually.
You can prefix adapt::*_trs format codes with adaptation
service name in curly braces to record response time(s) specific
to that service. For example: %{my_service}adapt::sum_trs

maximum_object_size_in_memory

Default size limit increased to 512KB.

negative_ttl

New default of 0 seconds. To prevent negative-caching of failure messages unless explicitly
permitted by the message generating web server.

Changing this is an RFC 2616 violation and now requires --enable-http-violations

refresh_pattern

New option 'ignore-must-revalidate'.

ignore-must-revalidate ignores any ``Cache-Control: must-revalidate``
headers received from a server. Doing this VIOLATES
the HTTP standard. Enabling this feature could make you
liable for problems which it causes.

New set of basic patterns. These should always be listed after any custom patterns.
They ensure RFC compliance with certain protocol and request handling in the absence
of accurate Cache-Control: and Expires: information.

This option causes some problems when bridging IPv4 and IPv6. A workaround has been provided.

Squid is built with a capability of bridging the IPv4 and IPv6 internets.
tcp_outgoing_address as previously used breaks this bridging by forcing
all outbound traffic through a certain IPv4 which may be on the wrong
side of the IPv4/IPv6 boundary.
To operate with tcp_outgoing_address and keep the bridging benefits
an additional ACL needs to be used which ensures the IPv6-bound traffic
is never forced or permitted out the IPv4 interface.
acl to_ipv6 dst ipv6
http_access allow to_ipv6 !all
tcp_outgoing_address 2002::c001 good_service_net to_ipv6
tcp_outgoing_address 10.0.0.2 good_service_net !to_ipv6
tcp_outgoing_address 2002::beef normal_service_net to_ipv6
tcp_outgoing_address 10.0.0.1 normal_service_net !to_ipv6
tcp_outgoing_address 2002::1 to_ipv6
tcp_outgoing_address 10.0.0.3 !to_ipv6

Build with support for loadable content adaptation modules.
Cannot be used with --disable-loadable-modules.

--enable-follow-x-forwarded-for

Support following the X-Forwarded-For HTTP header for determining the
original or indirect client when a request has been forwarded through other
proxies.

--enable-zph-qos

Build with support for ZPH Quality of Service controls

--disable-auto-locale

Disable error page localization for visitors.

error_directory option is required if this option is used.

--disable-caps

Build without libcap support. The default is to auto-detect system capabilities
and enable support when possible.

NOTE: Disabling this or building without libcap support will break TPROXY support.

--disable-ipv6

Build without IPv6 support. The default is to auto-detect system capabilities
and build with IPv6 when possible.

--disable-loadable-modules

Build without support for loadable modules.

--disable-strict-error-checking

Build Squid without advanced compiler error checking (without the -Werror option).
This only affects the building process, enabling it to complete despite some
possibly serious issues.
Please do not use lightly, and please report the build issues which make it needed
to the squid developers before doing so.

--disable-translation

Prevent Squid generating localized error page templates and manuals.
Which is usually tried, but may not be needed.

This is an optimization for building fast when localization is not needed
or localization tools are not available.

Enable CNAME recursion within the Internal DNS resolver stub squid uses.
This has no effect on the external DNS helper.

Please note this extension is still experimental and may encounter problems.
To see if it is actually needed you can run squid without it for a period and
check the CNAME-Only Requests statistics squid maintains.

If it produces ongoing serious problems the external helper may be needed
but please report the bugs anyway.

--with-libexpat / --without-libexpat

Require libexpat XML parser to be built into Squid for ESI parsing.
Build will fail if this option is used and the library is not present.
Default is to auto-detect it when using ESI and ignore if not present.
Use --without-libexpat to prevent it being auto-detected.

--with-libxml2 / --without-libxml2

Require libxml2 XML parser to be built into Squid for ESI parsing.
Build will fail if this option is used and the library is not present.
Default is to auto-detect it when building with ESI.
Use --without-libxml2 to prevent it being auto-detected.

--with-logdir=PATH

Allow build-time configuration of Default location for squid logs.

--with-ipv6-split-stack

Force enable special additions for IPv6 support in Windows XP and various BSD systems.
see the IPv6 details above for a better description.

--with-pidfile=PATH

Allow build-time configuration of Default location and name of squid.pid file.

--with-po2html=PATH

Absolute path to po2html executable.
Default is to automatically detect the binary.

This option now enables support for all three netfilter interception targets.

Adding TPROXY version 4+ support to squid through the netfilter TPROXY target.
This options requires a linux kernel 2.6.25 or later for embeded netfilter TPROXY targets.

Older REDIRECT and DNAT targets work as before on HTTP ports marked 'intercept'.

--enable-linux-tproxy

Deprecated. Remains only to support old TPROXY version 2.2 installations.
Scheduled for complete removal in Squid 3.2

--enable-ntlm-auth-helpers

Helper previously built by SMB is now built by smb_lm.
It also has a new squid.conf name for usage, see auth_param above for details.

--disable-internl-dns

Better support for Linux using the external DNS helper.
The helper will now compile and work with dns_nameservers on more variants of Linux than previously.
It is still deprecated however and use of this option should be avoided as much as possible.

--with-aio

Deprecated. POSIX AIO is now auto-detected and enabled.
Use --without-aio to disable, but only if you really have to.

--with-pthreads

Deprecated. pthreads library is now auto-detected and enabled.
Use --without-pthreads to disable, but only if you really have to.